Method for improved selective etching of silicon nitride over silicon oxide

Abstract

The present invention pertains to a method for etching at least one surface of a substrate, preferably for selectively etching silicon nitride, more preferably for selectively etching silicon nitride in the presence of silicon oxide.

Description

[0001] METHOD FOR IMPROVED SELECTIVE ETCHING OF SILICON NITRIDE OVER SILICON OXIDE

[0002] The present invention pertains to a method for etching at least one surface of a substrate, preferably for selectively etching silicon nitride, more preferably for selectively etching silicon nitride in the presence of silicon oxide.

[0003] BACKGROUND OF THE INVENTION

[0004] 3D memory devices are fabricated by vertically stacking multiple conductive silicon and insulating silicon dioxide layers alternatively. One of the fabrication steps involves selectively etching the sacrificial SiNx layer with an acidic etchant solution containing a variety of additives such as silanes, silicic acids, or unfunctionalized colloidal silica.

[0005] A high selectivity in etching is required to repeatedly remove vertical stacks of materials while maintaining the architecture of the chip. Colloidal silica as an additive has been postulated to provide corrosion resistance to silicon oxide in selective etching of silicon nitride over silicon oxide via the in situ formation of Si(OH)4 that reversibly suppresses silicon oxide etching according to Le Chatelier’s principle.

[0006] However, etching formulations comprising typical silica particles usually (i) introduce large silica particles to the etching chamber that in turn requires the presence of expensive filters in said chambers, and (ii) they still lack the required selectivity to minimize the loss of yield of semiconductor chips.

[0007] In the art, various attempts to use silicon oxide and / or silanes in etching formulations for above-described purpose have been reported. However, none of these approaches has been established in the industrial manufacturing to date.

[0008] JP 2021-015970 teaches a silicon nitride film etching solution for improving the etching selectivity of a silicon nitride film to a silicon oxide film, and a manufacturing method of a semiconductor device using silica having an amino acid-based, thioester-based, or ester-based group between the colloidal silica particles.

[0009] JP 2021-086943 describes the use of a composition of a silicon compound and phosphoric acid for selectively etching silicon nitride over silicon oxide.

[0010] US 2020 / 0308485 discloses an etching solution used for etching of silicon nitride. The etching solution includes: phosphoric acid; tetrafluoroboric acid; a silicon compound; water; and at least one of sulfuric acid and an ionic liquid. The silicon compound optionally comprises silica (claim 3, para 31).

[0011] US 2020 / 0216758 reports an etchant composition and a method of fabricating a semiconductor device, the composition including an inorganic acid; about 0.01 parts by weight to about 0.5 parts by weight of colloidal silica; about 0.01 parts by weight to about 30 parts by weight of an ammonium-based additive; and about 20 parts by weight to about 50 parts by weight of a solvent, all parts by weight being based on 100 parts by weight of the inorganic acid. US 2015 / 0111390 is directed at a method of selectively removing silicon nitride including: providing a wafer having silicon nitride on a surface of the wafer; providing a mixture of phosphoric acid and a silicon- containing material; and delivering the mixture to the surface of the wafer to remove the silicon nitride.

[0012] CN112216607 concerns a silicon nitride film etching solution comprising two different types of silica particles.

[0013] JP 2020-205320 proposes an additive for a silicon nitride etching solution, which contains an organic alkali silicate and water, and has a content of Na, K, Ca, Cr, Fe, and Cu of 1 mg / L or less.

[0014] While silanes or oligomers and polymers derived therefrom have also been used in the prior art, the compatibility of such compounds in the etching solutions remains a largely unresolved issue. Many of such etching solutions are of poor stability and / or lack from insufficient processability properties because the etching solutions are too viscous or inhomogeneous. It is fairly common that such etching solutions comprising silanes become more viscous over time, even to a point where they become unprocessable, or that the etching solution suffers from precipitation.

[0015] OBJECTIVE OF THE INVENTION

[0016] It is therefore the objective of the present invention to overcome the shortcomings of the prior art. It is a further objective of the present invention to provide a method for etching at least one surface of a substrate, preferably for selectively etching silicon nitride, more preferably for selectively etching silicon nitride in the presence of silicon oxide.

[0017] SUMMARY OF THE INVENTION

[0018] The aforementioned objectives are solved by the method according to the invention for etching at least one surface of a substrate, preferably for selectively etching silicon nitride, more preferably for selectively etching silicon nitride in the presence of silicon oxide, the method comprising the steps:

[0019] M1) providing the substrate having at least one surface; and

[0020] M2) treating the at least one surface of the substrate with a composition comprising a) at least one acid; b) at least one silica particle; characterized in that the at least one silica particle is at least partially functionalized with at least one silicon compound selected from the group consisting of organofunctional silane, organofunctional siloxane and mixtures of the aforementioned.

[0021] The composition of the method according to the invention is advantageously very stable and it thus can be used for a prolonged period of time. The method according to the invention surprisingly allows for very selective etchings of silicon nitride over silicon oxide. Using the inventive method, it is now possible to selectively remove silicon nitride in the presence of silicon oxide.

[0022] The method according to the invention advantageously allows for an improved ease of post-cleaning after its use, resulting in an overall more cleanly processing.

[0023] The method according to the invention allows for a higher etch rate of silicon nitride compared to prior art solutions.

[0024] The method according to the invention advantageously does not require any further additives to work as etching formulation, particularly as etching formulation for selectively removing silicon nitride in the presence of silicon oxide.

[0025] Preferred embodiments solving above-described objectives particularly well are described in the following description and in the dependent claims.

[0026] DETAILED DESCRIPTION OF THE INVENTION

[0027] Percentages throughout this specification are weight-percentages (wt.-% or weight-%) unless stated otherwise. Yields are given as percentage of the theoretical yield. Concentrations given in this specification refer to the mass of the entire solutions, dispersions or compositions unless stated otherwise. Room temperature means 20 °C. Standard pressure means 1013 mbar. Experiments were conducted at room temperature and standard pressure unless stated differently hereinafter. “At least one” in the context of the present invention means one or more than one, for example two.

[0028] The term "alkyl" according to the present invention comprises branched or unbranched alkyl groups comprising cyclic and / or non-cyclic structural elements, wherein cyclic structural elements of the alkyl groups naturally require at least three carbon atoms. C1-CX-alkyl in this specification and in the claims refers to alkyl groups having 1 to X carbon atoms (X being an integer). C1-C18-alkyl for example includes, among others, methyl, ethyl, n-propyl, iso-propyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, iso-pentyl, secpentyl, tert-pentyl, neo-pentyl, hexyl, heptyl and octyl, hexadecyl and octadecyl. The alkyl group is typically not substituted unless specified differently hereinafter.

[0029] The term "alkanediyl" is the corresponding group having two free valences (bonding sites). Sometimes, it is referred to as "alkylene" in the art. Said residues according to the present invention comprise cyclic and / or non-cyclic structural elements and can be linear and / or branched. C1-C4-alkanediyl for example includes, among others, methane-1 ,1-diyl, ethane-1 ,2-diyl, ethane-1 ,1-diyl, propane-1 ,3-diyl, propane-1 ,2- diyl, propane-1 ,1-diyl, butane-1 ,4-diyl, butane-1 ,3-diyl, butane-1 ,2-diyl, butane-1 ,1-diyl, butane-2,3-diyl. Usually, unless specified differently hereinafter, the alkanediyl group in not substituted. The "alkenyl" is an unsaturated alkyl group comprising at least one olefinic ( / .e. a C=C-double) bond.

[0030] Above-described details and preferences for the alkyl groups apply to alkenyl groups mutatis mutandis.

[0031] The term "aryl" according to the invention refers to ring-shaped aromatic hydrocarbon residues, for example phenyl or naphthyl. The aryl group is typically not substituted unless specified differently hereinafter. The term "alkaryl" according to the invention refers to hydrocarbon groups comprising at least one aryl and at least one alkyl group such as benzyl and p-tolyl. The bonding of such an alkaryl group to other moieties may occur via the alkyl or the aryl group of the alkaryl group. Above-described details and preferences for the alkyl and aryl groups apply for alkaryl groups mutatis mutandis.

[0032] If more than one residue - being it an atom, a group of atoms or entire building blocks - is to be selected from a given group, each of the residues is selected independently from each other unless stated otherwise hereinafter, meaning they can be selected to be the same members or different members of said group. The bonding sites in some chemical formulae herein may be emphasized by a wavy line (“ >AAAP“) as it is customary in the art.

[0033] Embodiments and preferences described for one aspect of the present invention apply mutatis mutandis to all the other aspects thereof unless technically unfeasible or stated otherwise. The repetition is omitted to improve the conciseness of the specification.

[0034] The composition used in the method according to the invention comprises (or preferably consists of) a) at least one acid; b) at least one silica particle; characterized in that the at least one silica particle is at least partially functionalized with at least one silicon compound selected from the group consisting of organofunctional silane, organofunctional siloxane and mixtures of the aforementioned.

[0035] The composition used in the method according to the invention comprises at least one acid. The at least one acid can be an inorganic or an organic acid. As organic acid, methane sulfonic acid is preferred. The at least one acid preferably is an inorganic acid. The at least one acid is preferably selected from the group consisting of sulfuric acid, phosphoric acid, polyphosphoric acid, phosphorous acid, hypophospho- rous acid, nitric acid, methane sulfonic acid and mixtures of the aforementioned. The at least one acid is more preferably selected from the group consisting of sulfuric acid, phosphoric acid, polyphosphoric acid, phosphorous acid, hypophosphorous acid, nitric acid, and mixtures of the aforementioned. Particularly preferably, the at least one acid is phosphoric acid.

[0036] The composition preferably comprises the at least one acid in an amount ranging from 20.0 to 99.9 wt.-%, more preferably from 30.0 to 90.0 wt.-%, even more preferably from 40.0 to 85.0 wt.-%, based on the total weight of the composition. The composition used in the method according to the invention comprises at least one silica particle.

[0037] The size (dso) of the at least one silica particle is preferably 1000 nm or less. The size (dso) of the at least one silica particle more preferably ranges from 5 to 500 nm, even more preferably from 5 to 200 nm, especially from 10 to 60 nm. The size of the at least one silica particle is measured by dynamic light scattering, preferably using the method described in the experimental section of this disclosure.

[0038] It is preferred that 20% or less of the at least one silica particles in the composition used in the method according to the invention are agglomerated, more preferably 10% or less, even more preferably 1 % or less. Ideally, all silica particles are discrete particles, / .e. they are not agglomerated.

[0039] The at least one silica particle comprises silica (SiO2). The at least one silica particle preferably consists of silica. The shape of the at least one silica particles is not further limited. It may be spherical, cocoon shaped (preferably having an aspect ratio ranging from 1 to 1.2), hexagonal or irregular.

[0040] The at least one silica particle is at least partially functionalized with at least one silicon compound. Functionalized means that the at least one silicon compound binds to surface of the at least one silica particle. By binding to the surface of the at least one silica particle, a layer is formed on the surface of the at least one silica particle. The layer may cover the entire surface of the at least one silica particle or only one or more parts thereof.

[0041] The organofunctional silane is preferably represented by formula (1):

[0042] R1

[0043] R2O- Si— OR2(1)

[0044] OR2wherein

[0045] R1is selected from the group consisting of amino-functional alkyl group and aryl group; and each R2is independently selected from the group consisting of hydrogen and C1-C4-alkyl group.

[0046] The aryl group of R1is preferably a phenyl group. The alkyl group of R1is preferably a C1-C4-alkyl group, more preferably a methyl group. More preferably, R1is selected from the group consisting of phenyl group and C1-C4-alkyl group. Even more preferably, R1is a phenyl group.

[0047] Each R2is preferably selected from the group consisting of methyl group and ethyl group.

[0048] Particularly preferably, the organofunctional silane is represented by formula (1 a): wherein each R2is independently selected from the group consisting of methyl group and ethyl group.

[0049] The organofunctional siloxane preferably comprises at least one building block according to formula (A): RA1

[0050] SiO[(3-n) / 2] (A)

[0051] (ORA2)nwherein

[0052] RA1is an amino-functional alkyl group; each RA2is independently selected from the group consisting of hydrogen and C1-C4-alkyl group; and n is selected from 0, 1 and 2.

[0053] The amino-functional alkyl group of RA1is preferably represented by formula (A-1):

[0054] (A-1) wherein each U is independently a C1-C8-alkanediyl group; each RA3and RA4are independently selected from the group consisting of hydrogen, C1-C4-alkyl group; and t is selected from 1 , 2 and 3.

[0055] Each U is preferably a C2-C4-alkanediyl group, more preferably a C2-C3-alkanediyl group. Each RA3and RA4is preferably selected from the group consisting of hydrogen and methyl group, more preferably each RA3and RA4is hydrogen, n is preferably 1 or 2, more preferably 1 .

[0056] Preferred amino-functional alkyl group for RA1are selected from the group consisting of

[0057] A particularly preferred version of said building block is represented by formula (A-2): wherein RA5is selected from the group consisting of hydrogen and -CH2-CH2-NH2 and n is selected from 0, 1 and 2.

[0058] It is preferred that the organofunctional siloxane comprises at least one building block according to formula (B) (in addition to the at least one building block according to formula (A)): wherein

[0059] RB1is selected from the group consisting of alkyl group and alkenyl group; each RB2is independently selected from the group consisting of hydrogen and C1-C4-alkyl group; and p is selected from 0, 1 and 2.

[0060] RB1is preferably selected from the group consisting of C1-C4-alkyl group and vinyl group. More preferably, RB1is a methyl group. Each RB2is preferably selected from the group consisting of hydrogen and methyl group, more preferably RB2is hydrogen.

[0061] The numerical ratio of the at least one building block according to formula (A) to the at least one building block according to formula (B) preferably ranges from 0.1 to 10, more preferably from 0.5 to 5, even more preferably from 1 to 1 .

[0062] The at least one building block according to formula (A) and - if contained in the organofunctional siloxane - the at least one building block according to formula (B) preferably make up for at least 50 weight-%, more preferably 75 weight-%, even more preferably 90 weight-%, of the organofunctional siloxane. The organofunctional siloxane most preferably consists of the one or more building blocks according to formula (A) and optionally, the one or more building blocks according to formula (B).

[0063] Preferably, the at least one organofunctional siloxane is an oligomer or a polymer. An improved crosslinking density of the film obtained from the organofunctional siloxane can then be obtained if the at least one organofunctional siloxane is an oligomer or a polymer. An oligomer according to the invention comprises (in total) 2 to 4 building blocks according to formulae (A) and (optionally) (B), a polymer comprises (in total) at least 5 building blocks according to formulae (A) and (optionally) (B). A non-limiting example of an oligomer comprising one building block according to formula (A) and one building block according to formula (B) is depicted hereinafter:

[0064] RA1RB1

[0065] RA2O— Si - O - Si- ORB2

[0066] ORA2ORB2

[0067] Oligomers and polymers usually comprise one or more of linear, branched and cyclic structures (said structures being formed by the building blocks according to formula (A) and / or (B)). The building blocks described herein can also be understood as structural repeating units if more than one building blocks according to formula (A) and optionally (B) is comprised by the organofunctional siloxane.

[0068] As used conventionally in the art, the Rg-SiO<4-g / 2) shall be understood that the depicted silicon atom carries 4-g oxygen atoms (g being an integer ranging from 0 to 4) and g residues R. The oxygen atoms are bound by a single bond to the silicon atom and thus have another substituent such as a silicon atom of a unity named above. In the case of the present invention, the other silicon atom is preferably one of a building block according to formula (A) or (B). If g is 3, a M-unit is present. If g is 2, a D-unit is present. If g is 1 , a T-unit is present. If g is 0, a Q-unit is present. This nomenclature is known to the person skilled in the art, e.g. from W. Noll, Chemie und Technologie der Silicone, Verlag Chemie, Weinheim Bergstr.,1960, p. 2 et seqq.

[0069] It is preferred that the silicon compound is selected from the group consisting of i) organofunctional silanes represented by the formula (1):

[0070] R1

[0071] R2O- Si— OR2(1)

[0072] OR2wherein

[0073] R1is selected from the group consisting of C1-C4-alkyl group and phenyl group; and each R2is independently selected from the group consisting of hydrogen and C1-C4-alkyl group; ii) organofunctional siloxanes comprising at least one building block according to formula (A) and optionally at least one building block according to formula (B); and mixtures of the aforementioned.

[0074] The weight of the layer formed by the at least one silicon compound on the surface of the at least one silica particle preferably makes up for 0.1 to 10.0 wt.-%, more preferably for 0.5 to 5.0 wt.-%, based on the total weight of the at least one silica particle.

[0075] Preferably, the composition used in the method according to the invention comprises the at least one silica particle in an amount ranging from 0.1 to 20.0 wt.-%, more preferably from 0.5 to 15.0 wt.-%, even more preferably from 1 .0 to 10.0 wt.-%, based on the total weight of the composition according to the invention.

[0076] The silica particle to be used in the composition used in the method according to the invention including the at least functionalization can be obtained by means known in the prior art. The silica particles can be synthesized by the Stober process using for example a tetraalkoxysilane, a base such as KOH or ammonia, water and a suitable solvent (e.g. ethanol). The functionalization of the silica particle can be obtained by treating the silica particle with the silicon compound. The functionalization can be carried out in a solvent (e.g. ethanol) using a catalyst (e.g. a base or an acid). These processes are well-established in the art. The functionalization can be carried out at a temperature ranging from 10 to 50 °C.

[0077] The duration of the funcationalization depends on various factors such as the temperature and any catalyst used during this procedure. Suitable durations range from 1 h to 24 h.

[0078] The composition used in the method according to the invention preferably comprises at least one surfactant. Preferable surfactants are (water-soluble) nonionic surfactants. The at least one surfactant is more preferably selected from the group consisting of polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether, polyoxyethylene C2-C22- alcohol ether, polyoxyethylene octyl phenyl ether, polyoxyethylene nonyl phenyl ether, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan trioleate, polyoxyethylene sorbit tetraoleate, polyethylene glycol onolaurate, polyethylene glycol monostearate, polyethylene glycol distearate, polyethylene glycol monooleate, polyoxyethylene alkylamine, polyoxyethylene hardened castor oil, alkylalkanolamide and mixtures thereof. Such surfactants are commercially available under the trade names Dynols and Surfynols.

[0079] Preferably, the composition used in the method according to the invention comprises the at least one surfactant in an amount ranging from 0.001 to 5 wt.-%, more preferably from 0.01 to 2.5 wt.-%, even more preferably from 0.1 to 1 wt.-%, based on the total weight of the composition according to the invention.

[0080] The composition used in the method according to the invention preferably comprises at least one solvent. The at least one solvent is preferably selected from the group consisting of water, alcohols, glycols and mixtures of the aforementioned.

[0081] Preferably, the composition used in the method according to the invention comprises the at least one solvent in an amount ranging from 0.1 to 50 wt.-%, more preferably from 1 to 30 wt.-%, even more preferably from 10 to 30 wt.-%, based on the total weight of the composition according to the invention.

[0082] The composition used in the method according to the invention preferably comprises at least one fluorine compound. The at least one fluorine compound is preferably selected from the group consisting of ammonium fluoride, tetra(C1-C6-alkyl)ammonium floride, hexafluorosilicic acid, ammonium tetrafluoro borate, tetra(C1-C6-alkyl)ammonium fluoride and tetrafluoroboric acid.

[0083] Preferably, the composition used in the method according to the invention comprises the at least one fluorine compound in an amount ranging from 0.0002 to 5 wt.-%, more preferably from 0.0005 to 2 wt.-%, even more preferably from 0.01 to 1 wt.-%, based on the total weight of the composition according to the invention.

[0084] The composition used in the method according to the invention preferably comprises at least one polysilicon corrosion inhibitor. The at least one polysilicon corrosion inhibitor is preferably selected from the group consisting of linear and branched C8-C16-alkylbenzenesulfonic acids. More preferably, the at least one polysilicon corrosion inhibitor is selected from the group consisting of octylbenzenesulfonic acid, nonylalkylbenzenesulfonic acid, decylbenzesulfonic acid, undecylbenzenesulfonic acid, dodecylbenzenesulfonic acid, tridecylbenzenesulfonic acid, tetradecylbenzenesulfonic acid, tetradecylbenzenesulfonic acid, pentadecylbenzenesulfonic acid, hexadecylbenzenesulfonic acid, heptadecylbenzesulfonic acid, octadecylbenzenesulfonic acid. As an alternative to aforementioned C8-C16-alkylbenzenesulfonic acids, C6-C16-alkyldiphenyl sulfide disulfonic acids, and C6-C16-alkyldiphenylamine disulfonic acids may be used. Preferably, the composition used in the method according to the invention comprises the at least one polysilicon corrosion inhibitor in an amount ranging from 0.001 to 5 wt.-%, more preferably from 0.01 to 2 wt.-%, even more preferably from 0.02 to 0.08 wt.-%, based on the total weight of the composition according to the invention.

[0085] The composition used in the method according to the invention preferably comprises (or consists of) a) the at least one acid; b) the at least one silica particle; c) the at least one surfactant; d) the at least one solvent; e) the at least one fluorine compound; and f) optionally, the at least one polysilicon corrosion inhibitor; characterized in that the at least one silica particle is at least partially functionalized with at least one silicon compound selected from the group consisting of organofunctional silane, organofunctional siloxane and mixtures of the aforementioned.

[0086] In one embodiment of the present invention, the composition used in the method according to the invention preferably comprises (or consists of) a) the at least one acid; b) the at least one silica particle; c) the at least one surfactant; d) the at least one solvent; e) the at least one fluorine compound; and f) optionally, the at least one polysilicon corrosion inhibitor; characterized in that the at least one silica particle is at least partially functionalized with at least one silicon compound selected from the group consisting of organofunctional silane, organofunctional siloxane and mixtures of the aforementioned wherein the at least one silicon compound is selected from the group consisting of organofunctional silane is represented by formula 1a and organofunctional siloxane comprising at least one building block according to formula A-2.

[0087] The composition used in the method according to the invention can be prepared by standard means known to the person skilled in the art. It is preferably prepared by mixing the components of the composition using standard equipment such as stirrers and suitable vessels.

[0088] The present invention concerns a method of etching at least one surface of a substrate, preferably for selectively etching silicon nitride, more preferably for selectively etching silicon nitride in the presence of silicon oxide, comprising the method steps:

[0089] M1) providing the substrate having the at least one surface; and

[0090] M2) treating the at least one surface of the substrate with the composition described above. By treating the at least one surface of the substrate with the composition described above, an etched surface is obtained. The inventive method comprises method steps M1 and M2. The method steps are carried out in the given order. It optionally comprises further method steps to be included in the inventive method before, between or after method steps M1 and M2.

[0091] The substrate preferably is a semiconductor substrate, more preferably selected from the group consisting of sensors, memory logic device substrates and semiconductor packaging material. Preferable sensors are MEMS (micro-electromechanical systems). Memory logic device substrates are inter alia RAMs such as CBRAM, ReRAM, PCM, FeRAM and Memory (NAND and DRAM). Semiconductor packaging material in the context of the present invention are - among others - IC substrates and printed circuit boards.

[0092] The method according to the invention is preferably used to etch silicon nitride. It is preferred that the silicon nitride and silicon oxide are (both) present on the surface of the substrate. The method advantageously allows for a selective etching of one of silicon nitride and silicon oxide over the other of the aforementioned, usually silicon nitride over silicon oxide.

[0093] The method according to the invention preferably comprises a further method step M1 a to be carried out between method steps M1 and M2:

[0094] M1 a) treating the at least one surface of the substrate with at least one pretreatment compound wherein the at least one pretreatment compound is selected from the group consisting of:

[0095] - one or more silanes according to formula (X):

[0096] RX1

[0097] RX2O— Si— ORX2(X)

[0098] ORX2wherein

[0099] RX1is an organofunctional radical, RX1is preferably selected from the group consisting of C1-C4- alkyl group and phenyl group; and each RX2is independently selected from the group consisting of hydrogen and C1-C4-alkyl group; and

[0100] - one or more siloxanes comprising at least one building block according to formula (Y-1):

[0101] RY1

[0102] SiO[(3.y) / 2] (Y)

[0103] (ORY2)ywherein

[0104] RY1is an amino-functional alkyl group; each RY2is independently selected from the group consisting of hydrogen and C1-C4-alkyl group; and y is selected from 0, 1 and 2: and optionally, at least one building block according to formula (Z) (in addition to the at least one building block according to formula (A)):

[0105] RZ1

[0106] SiO[(3.Z) / 2] (Z)

[0107] (ORZ2)Zwherein

[0108] RZ1 is selected from the group consisting of alkyl group and alkenyl group, preferably a C1-C4- alkyl group, more preferably a methyl group, n-propyl group or a / so-butyl group, even more preferably a / so-butyl group; each RZ2is independently selected from the group consisting of hydrogen and C1-C4-alkyl group, preferably selected from the group consisting of hydrogen and methyl group, more preferably RZ2is hydrogen; and z is selected from 0, 1 and 2.

[0109] The combination of method step M1 a and M2 (i.e. the use of the composition described above) results in a synergistic effect (see examples 2a to 2c in the experimental section). The combination of the pretreatment compound and the composition described above gives much higher selectivities than the additive effects of the two individual treatments would suggest.

[0110] The aryl group of RX1is preferably a phenyl group. The alkyl group of RX1is preferably a C1-C4-alkyl group, more preferably a methyl group. More preferably, RX1is selected from the group consisting of phenyl group and C1-C4-alkyl group. Even more preferably, RX1is a phenyl group.

[0111] The amino-functional alkyl group of RY1is preferably represented by formula (Y-1):

[0112] (Y-1) wherein each V is independently a C1-C8-alkanediyl group; each RX3and RX4are independently selected from the group consisting of hydrogen, C1-C4-alkyl group; and x is selected from 1 , 2 and 3.

[0113] Each V is preferably a C2-C4-alkanediyl group, more preferably a C2-C3-alkanediyl group. Each RX3and RX4is preferably selected from the group consisting of hydrogen and methyl group, more preferably each RX3and RX4is hydrogen, y is preferably 1 or 2, more preferably 1 . x is preferably 1 or 2, more preferably 1. Preferred amino-functional alkyl group for RY1are selected from the group consisting of

[0114] In method step M2, the at least one surface of the substrate is treated with the composition described above.

[0115] The temperature in method step M2 preferably ranges from 100 to 200 °C, more preferably from 120 to 180 °C, even more preferably from 140 to 170 °C.

[0116] The duration of method step M2 is not further limited and person skilled in the art can select suitable durations based on routine experiments. Generally, durations of method step M2 ranging from 1 s to 360 min, preferably from 30 s to 240 min, more preferably from 1 min to 120 min, have proven useful.

[0117] Preferably, the inventive method comprises method step M3 to be included after method step M2: M3) rinsing the treated substrate with water.

[0118] Method step M3 aims to remove any residual components of the comprising described above, in particular the acid, from the surface of the substrate. Method step M3 reduces the risk of derogation of any residual components on the surface of the substrate during subsequent manufacturing steps.

[0119] In method step M3, the water is preferably deionized. The temperature of the water in method step M3 preferably ranges from 5 to 50 °C, more preferably from 10 to 30 °C. The duration of method step M3 preferably ranges from 1 s to 120 s, preferably from 5 to 30 s.

[0120] It is particularly preferred to use an organofunctional silane according to formula X wherein RX1represents a phenyl group in method step M1 a and to use silica particle at least partially functionalized with organofunctional siloxane comprising at least one building block according to formula (A) wherein aminofunctional alkyl group for RY1are selected from the group consisting of anc| , , and at least one building block according to formula (B) wherein RZ1is a n-propyl group or an iso-butyl group.

[0121] Another aspect of the present invention pertains to the use of the composition described above to selectively etch silicon nitride, preferably for selectively etching silicon nitride in the presence of silicon oxide. Also disclosed is a semiconductor substrate having been treated with the composition described above. The semiconductor substrate is preferably selected from above-defined groups.

[0122] The present invention is further described by the following items:

[0123] 1 . A composition for etching at least one surface of a substrate, preferably for selectively etching silicon nitride, more preferably for selectively etching silicon nitride in the presence of silicon oxide, the composition comprising: a) at least one acid; b) at least one silica particle; characterized in that the at least one silica particle is at least partially functionalized with at least one silicon compound selected from the group consisting of organofunctional silane, organofunctional siloxane and mixtures of the aforementioned.

[0124] 2. The composition according to item 1 characterized in that the organofunctional silane is represented by the formula (1):

[0125] R1

[0126] R2O- Si— OR2(1)

[0127] OR2wherein

[0128] R1is selected from the group consisting of amino-functional alkyl group and aryl group; and each R2is independently selected from the group consisting of hydrogen and C1-C4-alkyl group.

[0129] 3. The composition according to iterm 1 or 2 characterized in that the organofunctional siloxane comprises at least one building block according to formula (A):

[0130] RA1

[0131] SiO[(3-n) / 2] (A)

[0132] (ORA2)nwherein

[0133] RA1is an amino-functional alkyl group; each RA2is independently selected from the group consisting of hydrogen and C1-C4-alkyl group; and n is selected from 0, 1 and 2.

[0134] 4. The composition according to item 3 characterized in that the organofunctional siloxane comprises at least one building block according to formula (B): wherein

[0135] RB1is selected from the group consisting of alkyl group and alkenyl group; each RB2is independently selected from the group consisting of hydrogen and C1-C4-alkyl group; and p is selected from 0, 1 and 2. The composition according to item 4 characterized in that the numerical ratio of the at least one building block according to formula (A) to the at least one building block according to formula (B) ranges from 0.1 to 10, preferably from 0.5 to 5, more preferably from 1 to 1 . The composition according to any one of the preceding items characterized in that the at least one acid is selected from the group consisting of sulfuric acid, phosphoric acid, polyphosphoric acid, phosphorous acid, hypophosphorous acid, nitric acid, methane sulfonic acid and mixtures of the aforementioned. The composition according to item 6 characterized in that the at least one acid is phosphoric acid. The composition according to any one of the preceding items characterized in that the composition comprises the at least one silica particle in an amount ranging from 0.1 to 20.0 wt.-%, preferably from 0.5 to 15.0 wt.-%, more preferably from 1 .0 to 10.0 wt.-%, based on the total weight of the composition. The composition according to any one of the preceding items characterized in that the composition comprises the at least one acid in an amount ranging from 20.0 to 99.9 wt.-%, preferably from 30.0 to 90.0 wt.-%, more preferably from 40.0 to 85.0 wt.-%, based on the total weight of the composition. The composition according to any one of the preceding items characterized in that the composition comprises at least one surfactant, at least one solvent, at least one fluorine compound, and optionally, at least one polysilicon corrosion inhibitor. A method of etching at least one surface of a substrate, preferably for selectively etching silicon nitride, more preferably for selectively etching silicon nitride in the presence of silicon oxide, comprising the method steps:

[0136] M1) providing the substrate having the at least one surface; and

[0137] M2) treating the at least one surface of the substrate with the composition according to any one of the preceding items. The method according to item 1 1 characterized in that the substrate is a semiconductor substrate, preferably selected from the group consisting of memory logic device substrates and semiconductor packaging material. 13. The method according to any one of items 11 or 12 characterized in that the silicon nitride and silicon oxide are present on the surface of the substrate.

[0138] 14. Use of the composition according to any one of items 1 to 10 to selectively etch silicon nitride, preferably for selectively etching silicon nitride in the presence of silicon oxide.

[0139] 15. A semiconductor substrate having been treated with the composition according to any one of items 1 to 10.

[0140] The invention will now be illustrated by reference to the following non-limiting examples.

[0141] EXAMPLES

[0142] Commercial products were used as described in the technical datasheet available on the date of filing of this specification unless stated otherwise hereinafter. The most recent versions of standards were used unless stated differently hereinafter.

[0143] The pH value was measured in accordance to DIN EN ISO 10523 (2012).

[0144] The size of the at least one silica particles was measured as follows: in a 1 cm x 1 cm polystyrene cuvette, 40 microliters of colloidal silica solution was dispersed in 1 ml of deionized water. The cuvette was then placed in a Malvern Zetasizer ultra Dynamic light scattering instrument to measure the Z-average of the suspended colloidal silica particles.

[0145] The following silanes and siloxanes were used throughout the experiments: a. phenyltriethoxysilane (hereinafter silane 1) b. a siloxane prepared as described in example 1 of US 10,259,832 (hereinafter siloxane 1) c. a siloxane prepared as described in example 5 of US 5,629,400 (hereinafter siloxane 2)

[0146] The normalized silicon oxide etch rate (referred to as “Normalized SiOx etch rate” in below tables) was measured as follows: [thickness difference of silicon oxide per unit time with silicon compound] / [thickness difference of silicon oxide per unit time without silicon compound]

[0147] The normalized silicon nitride etch rate (referred to as “Normalized SiNx etch rate” in below tables) was measured as follows: [thickness difference of silicon nitride per unit time with silicon compound] / [ thickness difference of silicon nitride per unit time without silicon compound]

[0148] The selectivity ratios (SiNx / SiOx) in below tables are the quotient of the normalized silicon nitride etch rate by the normalized silicon oxide etch rate.

[0149] The selectivity differences (|SiNx| - |SiOx|) are calculated by subtracting the absolute value of the normalized silicon oxide etch rate from the absolute value of the normalized silicon nitride etch rate.

[0150] Example 1 : silane functionalized colloidal silica in etching medium (inventive procedure)

[0151] A 20 ml solution of 20 wt% colloidal silica, with a size (dso) of 50 nm, was surface modified by adding 2 g silicon compound (10 wt% of colloidal silica solution, see table 1 , column denominated “Silicon compound on colloidal silica”) to the colloidal silica solution and left to stir overnight at 20 °C. To prepare the etching solution, 0.25 g of the functionalized colloidal silica was placed in 4.75 g of 85% Phosphoric acid (concentration of colloidal silica in the etching solution was 1 wt%). The solution was heated to 160 °C, then an area of 1x1 cm2of a 1 x 3 cm2wafer strip was placed in the etching solution for 1 hr. Afterwards, the wafer was removed from the etching solution, then submerged in water to remove any residual etching solution.

[0152] As alternative, comparative examples 1 a and 1 b were carried out by using an etching solution without silica particles. The etching solution in the comparative examples was prepared by mixing 85 wt.-% phosphoric acid (aq.) and the silicon compound listed in the column denominated “Additive silicon compound" in below table.

[0153] Table 1

[0154] * comparative example; ° inventive example

[0155] Obviously, the selectivity of the etching was significantly improved when using the composition according to the invention (see inventive examples 1 c and 1d compared to comparative examples 1 a and 1 b).

[0156] When silanes were merely added to the etchant as in the comparative examples, the selectivity was about three times inferior compared to the inventive examples using the very same compounds.

[0157] Example 2: Precoated substrate and silane functionalized colloidal silica in etching medium

[0158] Silicon oxide or nitride wafer is placed into an aqueous solution with 10 wt.-% of silane at 20 °C for 24 h. A 20 ml solution of 20 wt% colloidal silica, with a size (dso) of 50 nm, was surface modified by adding 2 g silicon compound (10%wt of colloidal silica solution, see table 2, column denominated “Silicon compound on colloidal silica”) to the colloidal silica solution and left to stir overnight at 20 °C. To prepare the etching solution, 0.25 g of the functionalized colloidal silica was placed in 4.75 g of 85% Phosphoric acid (concentration of colloidal silica in the etching solution is 1 wt.-%). The solution was heated to 160 °C, then the surface modified wafer with dimensions 1x1 cm was placed in the etching solution for 1 h. Afterwards, the wafer was removed from the etching solution, then submerged in water to remove any residual etching solution.

[0159] Table 2

[0160] * comparative example; ° inventive example

[0161] The inventive compositions allow for an improved etching selectivity of silicon nitride over silicon oxide as can be derived from the data above. Notably, said selectivity is improved over using unfunctionalized silica in the etching formulation as outlined in the prior art (compare comparative example 2a and inventive example 2c). From the data above, it can be seen that a synergy of the precoating and the composition according to the invention exists.

Claims

Claims1. A method of etching at least one surface of a substrate, preferably for selectively etching silicon nitride, more preferably for selectively etching silicon nitride in the presence of silicon oxide, comprising the method steps:M1) providing the substrate having the at least one surface; andM2) treating the at least one surface of the substrate with a composition comprising: a) at least one acid; b) at least one silica particle; characterized in that the at least one silica particle is at least partially functionalized with at least one silicon compound selected from the group consisting of organofunctional silane, organofunctional siloxane and mixtures of the aforementioned.

2. The method according to claim 1 , characterized in that the organofunctional silane is represented by the formula (1):R1R2O- Si— OR2(1)OR2whereinR1is selected from the group consisting of amino-functional alkyl group and aryl group; and each R2is independently selected from the group consisting of hydrogen and C1-C4-alkyl group.

3. The method according to claim 1 or 2, characterized in that the organofunctional siloxane comprises at least one building block according to formula (A):RA1SiO[(3-n) / 2] (A)(ORA2)nwhereinRA1is an amino-functional alkyl group; each RA2is independently selected from the group consisting of hydrogen and C1-C4-alkyl group; and n is selected from 0, 1 and 2.

4. The method according to claim 3, characterized in that the organofunctional siloxane comprises at least one building block according to formula (B):whereinRB1is selected from the group consisting of alkyl group and alkenyl group; each RB2is independently selected from the group consisting of hydrogen and C1-C4-alkyl group; and p is selected from 0, 1 and 2.

5. The method according to claim 4, characterized in that the numerical ratio of the at least one building block according to formula (A) to the at least one building block according to formula (B) ranges from 0.1 to 10, preferably from 0.5 to 5, more preferably from 1 to 1 .

6. The method according to any one of the preceding claims, characterized in that the at least one acid is selected from the group consisting of sulfuric acid, phosphoric acid, polyphosphoric acid, phosphorous acid, hypophosphorous acid, nitric acid, methane sulfonic acid and mixtures of the aforementioned.

7. The method according to claim 6, characterized in that the at least one acid is phosphoric acid.

8. The method according to any one of the preceding claims, characterized in that the composition comprises the at least one silica particle in an amount ranging from 0.1 to 20.0 wt.-%, preferably from 0.5 to 15.0 wt.-%, more preferably from 1 .0 to 10.0 wt.-%, based on the total weight of the composition.

9. The method according to any one of the preceding claims, characterized in that the composition comprises the at least one acid in an amount ranging from 20.0 to 99.9 wt.-%, preferably from 30.0 to 90.0 wt.-%, more preferably from 40.0 to 85.0 wt.-%, based on the total weight of the composition.

10. The method according to any one of the preceding claims characterized in that the composition comprises at least one surfactant, at least one solvent, at least one fluorine compound, and optionally, at least one polysilicon corrosion inhibitor.

11. The method according to any one of the preceding claims, characterized in that the substrate is a semiconductor substrate, preferably selected from the group consisting of memory logic device substrates and semiconductor packaging material.

12. The method according to any one of the preceding claims, characterized in that the silicon nitride and silicon oxide are present on the surface of the substrate.

13. Use of the composition according to any one of claims 1 to 10 to selectively etch silicon nitride, preferably for selectively etching silicon nitride in the presence of silicon oxide.

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